Canon 60D has a 18.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features Digic 4 processor. On the other hand, Canon 750D has a 24.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features DIGIC 6 processor. Canon 750D's sensor provides 6MP more than Canon 60D's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the 60D and 750D sensor size comparison.
Canon 60D and Canon 750D have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Canon 60D has 33% larger pixel area compared to Canon 750D, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.